Epithelial Tissue: Types and Characteristics

• Tissue represents a level of biological organization between cells and organs.
• A tissue consists of similar cells and their extracellular matrix, all cooperating to perform a specific function.

Types of Tissues

• The four basic tissue types are epithelial, connective, muscle, and nervous tissue.
• Epithelial tissue covers surfaces, lines cavities, and forms glands.
• Connective tissue supports other tissues structurally and functionally.
• Muscle tissue facilitates body movement.
• Nervous tissue enables communication throughout the body.

Epithelial Tissue

• Epithelial tissues are widespread in the body.
• They cover body surfaces, line cavities and organs, and constitute the primary tissue within glands.
• Functions include protection, secretion, absorption, excretion, filtration, diffusion and sensory reception.

Characteristics of Epithelial Tissue

• Cellularity: Epithelial tissues are composed almost entirely of cells.
• Special Contacts: Cells are closely packed to form continuous sheets.
• Polarity: Tissues exhibit an apical (free) and a basal (attached) surface.
• Support: Supported by underlying connective tissue.
• Avascularity: Epithelial tissues lack blood vessels but are innervated.
• Regeneration: High regenerative capacity.

Classification of Epithelial Tissue

• Classified by cell shape and number of cell layers.
• Cell shapes: squamous (flattened), cuboidal (cube-shaped), or columnar (column-like).
• Cell layers: simple (one layer) or stratified (multiple layers).
• These criteria combine to form names like simple squamous epithelium and stratified cuboidal epithelium.

Connective Tissue

• Connective tissue is the most abundant and widely distributed of the primary tissues.
• Functions: binding, support, protection, insulation, and transportation (e.g., blood).

Characteristics of Connective Tissue

• Common origin: All connective tissues originate from mesenchyme (an embryonic tissue).
• Varying degrees of vascularity: Ranges from avascular to highly vascularized.
• Extracellular matrix: Predominantly nonliving, separates tissue cells.

Components of Extracellular Matrix

• Ground substance: Unstructured material filling spaces between cells and housing fibers.
• Fibers: Includes collagen, elastic, and reticular fibers.
• Collagen fibers: High tensile strength.
• Elastic fibers: Enable recoil after stretching.
• Reticular fibers: Form delicate networks.
• Cells: Major connective tissue classes have characteristic cell types.
• Connective tissue proper: fibroblast.
• Cartilage: chondroblast.
• Bone: osteoblast.
• Blood: hematopoietic stem cell.

Types of Connective Tissue

• Connective tissue proper: loose (areolar, adipose, reticular) and dense (dense regular, dense irregular, elastic).
• Cartilage: hyaline, elastic, and fibrocartilage.
• Bone tissue.
• Blood.

Muscle Tissue

• Muscle tissue is specialized for contraction, which produces movement.
• There are three types: skeletal, cardiac, and smooth.

Skeletal Muscle Tissue

• It is attached to bones and is responsible for body movement.
• Skeletal muscle cells are long, cylindrical, multinucleate, and striated.

Cardiac Muscle Tissue

• Exclusively found in the heart.
• Cardiac muscle cells are uninucleate, striated, branched, and connected by intercalated discs.

Smooth Muscle Tissue

• Located in the walls of hollow organs.
• Smooth muscle cells are spindle-shaped, uninucleate, and nonstriated.

Nervous Tissue

• It forms the nervous system, which regulates and controls body functions.
• Composed of neurons and neuroglia.

Neurons

• Specialized cells that generate and conduct electrical signals.

Neuroglia

• Supporting cells that provide physical support, insulation, and protection for neurons.

Learn about epithelial tissue, one of the four basic types of tissues in the body. Epithelial tissues cover body surfaces, line body cavities, and form glands. This tissue type performs functions such as protection, secretion, absorption, and filtration.